1. Field of the Invention
The present invention relates to an electronic parts casing for high-frequency equipment such as a tuner.
2. Description of the Related Art
A conventional electronic parts casing will be described with reference to FIGS. 3 and 4. FIGS. 3 and 4 show a conventional electronic parts casing 100, which consists of a frame member 1 and inner and outer covers 2 and 3 covering the top of the frame member. The frame member 1 is divided into chambers 40 by a partition 1a provided inside the frame member 1. The frame member 1 includes edges 4 having tongues 5 for fastening the inner cover 2 and the outer cover 3. Further, two outwardly convex draw surfaces 6 are provided in correspondence with the two chambers 40, the area of each draw surface 6 being smaller than that of the corresponding chamber 40.
As shown in FIG. 4, the electronic parts casing 100 is formed as follows: the inner cover 2 is brought into contact with the edges 4 of the frame member 1, and the outer cover 3 is placed on the inner cover 2 to cover the same. The draw surfaces 6, provided on the inner cover 2, are brought into close contact with the inner surface of the outer cover 3, and the tongues 5 provided on the frame member 1 are inserted into cutouts 8 and through-holes 7 provided in the inner cover 2 and the outer cover 3. Then, the tongues 5 are twisted, whereby the inner cover 2 and the outer cover 3 are engaged with and fixed to the frame member 1.
The electronic parts casing 100 has a double structure, which is composed of the inner cover 2 to be brought into contact with the edges 4 of the frame member 1, and the outer cover 3 provided to be pressed against the inner cover 2. The frame member 1 is divided into two chambers 40 by a partition, and an electronic part (not shown), such as a tuner substrate, is accommodated in each chamber 40.
Generally speaking, in an electronic parts casing, it is necessary to shield the chambers from each other in order that a radio wave signal generated from one electronic part, such as a tuner, may not affect other electronic parts. In this electronic parts casing 100, the inner cover 2 and the edges 4 of the frame member 1 and of the partition 1a are completely held in close contact with each other due to the resilient force generated by the close contact of the draw surfaces 6 of the inner cover 2 with the inner surface of the outer cover 3, so that a radio wave signal or the like generated from an electronic part in one chamber 40 is not allowed to leak to the other chamber.
However, the conventional electronic parts casing 100, described above, has the following problems:
In the electronic parts casing 100, when engaging the frame member 1 with the inner cover 2 and the outer cover 3 or when detaching the inner cover 2 and the outer cover 3 from the frame member 1, the tongues 5 are twisted, so that it takes a lot of man-hours to assemble the casing 100. In particular, when repairing the electronic parts in the casing 100, the tongues 5 are twisted reversely to remove the inner cover 2 and the outer cover 3, and, after the repair, the tongues 5 are twisted again for engagement. This operation takes a lot of time. Further, due to the deterioration in the strength of the base portions of the tongues 5 and the deformation of the tongues 5, the inner cover 2 and the outer cover 3 cannot be completely fixed.
Further, due to the provision of the tongues 5, which protrude from the frame member 1, there is a limitation in the possible reduction of size. Further, when stamping out the frame member 1 from a metal plate (not shown), it is necessary to stamp out the tongues 5, with the result that a lot of time is required. Further, a surplus area of the metal plate is required, resulting in a rather high cost.
FIGS. 5 and 6 show an electronic parts casing 110 in which the above problems have been solved.
The electronic casing 110 shown in FIGS. 5 and 6 are composed of a frame member 10, and inner and outer covers 11 and 12 covering the top of the frame member. Of these, the frame member 10 is divided into a plurality of chambers 41 by a partition 10a provided inside the frame member 10. On the outer side surfaces of the frame member 10, there are provided ridges 14 for the engagement of the outer cover 12. In the periphery of the outer cover 12, there are provided detents 15 to be engaged with the ridges 14 provided on the side surfaces of the frame member 10. Further, on the top surface of the inner cover 11, there are provided outwardly convex draw surfaces 16 in correspondence with the two chambers 41, the area of each draw surface being smaller than that of the corresponding chamber 41.
As shown in FIG. 6, in the electronic parts casing 110, the inner cover 11 is placed on the frame member 10 such that it is in contact with the edges 17 of the frame member 10 and of the partition 10a. The outer cover 12 is placed on the inner cover 11, and the draw surfaces 16 provided on the inner cover 11 are brought into close contact with the inner surface of the outer cover 12. The detents 15 provided on the outer cover 12 are engaged with the ridges 14 provided on the frame member 10, whereby the outer cover 12 is engaged with and fixed to the frame member 10 from above the inner cover 11.
In the electronic parts casing 110, constructed as described above, the above-mentioned problems of the electronic parts casing 100 have been eliminated. However, it has the following problems:
In the electronic parts casing 110, the detents 15 provided on the outer cover 12 are engaged with the ridges 14 provided on the frame member 10, and the outer cover 12 is engaged with and fixed to the frame member 10 from above the inner cover 11. In this construction, the frame member 10 is subject to deformation due to the load applied to the ridges 14. Further, as a result of the deformation of the frame member 10, there is a concern that the electronic parts (not shown) in the frame member 10 will be damaged.
According to a method for preventing such deformation of the frame member 10, the thickness of the outer cover 12 is made smaller than that of the frame member 10. In this case, however, it is generally necessary for the outer cover to be formed in a thickness ranging from approximately 0.2 to 0.4 mm. In the case of a metal plate of this thickness (e.g., iron plate), deformation, such as warpage, is liable to be generated during working. When the outer cover 12 thus formed is used in the electronic parts casing 110, the resilient force generated from the close contact between the draw surfaces 16 of the inner cover 11 and the inner surface of the outer cover 12 is degenerated by the deformation, with the result that the close contact between the inner cover 11 and the edges 17 of the frame member 10 and of the partition 10a is cancelled, resulting in the RF signal, etc. generated by the electronic part in one chamber 41 leaking into the other chamber.